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The relationship between adipose tissue and bone mineral density (BMD) is complex and depends on multiple factors. Body weight is con sidered a protective factor in bone health and, on the contrary, a low body mass index (BMI) is known as a risk factor in fragility fracture1,2. Although osteoporosis diagnosis is done by deter mining the BMD by dual-energy X-ray absorptio metry (DXA), most fragility fractures are suffered by individuals without densitometric osteoporosis3. Research carried out on obese patients showed positive associations between weight and BMD (both; areal and volumetric), as well as higher cortical thickness and a greater number of trabeculae4. Despite these findings, the bene ficial effect may vary in different skeletal sites, with an increase in fractures in peripheral sites such as the radius and lower extremities5. These results reveal the existence of multiple factors involved in the physio pathogenesis of fractures in obese patients.
The purpose of this research is to assess the relationship between adipose tissue, its location and spine and hip BMD in women over the age of 60 in a reference center in Argentina.
This is a cross-sectional, study. It was carried out consecutively on postmenopausal women over 60 years old with referrals for body compo sition assessment and muscle strength tests in a specialized medical center in Buenos Aires since 2018. To take part in the research, they needed a spine and hip bone density test from 24 months prior to the study. All measurements were ob tained by the same specialized technician. The study was conducted according to the Declara tion of Helsinki. Written informed consent was obtained from all participant.
Determinations
Information was obtained on previous BMD (g/cm2) on spine and hip (femoral neck and to tal hip), and T-score. In order to define osteo porosis, the classification proposed by the World Health Organization in 2004 has been used, with T-score ≤ -2.5 in any of the assessed areas.
Anthropometric measurements were evalua ted during the body composition assessment. Weight was measured with mechanical scales of 0.1 kg accuracy, and height was measured with a wall stadiometer of 0.5 cm accuracy. BMI was calculated with Quetelet’s index (weight/ height2).
Body composition assessment was carried out with DXA equipment, Lunar Prodigy Advan ce (GE- Lunar, Madison, WI, USA), with enCORE software. For this purpose, the positioning of pa tients and regions of interest were determined according to the manufacturer’s standards and the International Society for Clinical Densito metry (ISCD) guidelines. CoreScan was used to measure VAT (gr and cm3).
Adipose tissue compartment
Total body fat mass was calculated in grams and %. Android and gynoid regional body fat were calculated in % and later the fat mass in dex (FMI) was assessed (total fat/height2) as well as the A/G ratio. Visceral adipose tissue (VAT) was measured in mass (g) and volume (cm3). For this assessment, the region of interest pro vided by the manufacturer was used, in a 10 cm long area from the superior border of the iliac crest.
Skeletal muscle mass
Total skeletal muscle mass and upper and lower extremities muscle mass (appendicular muscle mass or AMM) were calculated by means of DXA.
Statistics
Quantitative variables were expressed as ave rage and standard deviation (±SD). According to their distribution, the statistical analysis of wo men with and without osteoporosis in any as sessed region was carried out by using Student’s t-distribution and the Wilcoxon-Mann-Whitney test. Variable associations were obtained with the Pearson Correlation Coefficient. We considered a statistical significance of p-value ≤ 0.05. IBM SPSS Statistics (Version 27) was used for the analysis.
In total, 156 women took part in this study. The average age was 68.5±5.6 years old (60-89 years old age range). The average BMI was 24.87 ± 3.98. When classifying the samples into osteoporotic n= 74 (47%) vs. non-osteoporotic n = 84 (53%), it was clear that the second group shows higher values in: Total fat tissue (27513.99 ± 6862.83 vs. 24189.15 ± 7208.52 grams, p = 0.0037), VAT (599.23 ± 526.04 vs. 727.76 ± 545.25 g, p = 0.0426), BMI and FMI (Table 1). A simple correlation analysis showed a positive but small correlation between VAT and BMD Lumbar Spine r = 0.30; p < 0.05, VAT vs. BMD Total Hip r = 0.24; p < 0.05; VAT vs. BMD Femoral Neck r = 0.32; p < 0.05.
The high frequency of osteoporosis in our sample is a consequence of being a reference center for bone metabolism. Our study showed that women with osteoporosis had less visceral adipose tissue and fat mass than women without osteoporosis. Similar findings were re cently published by Liu et al., who found a po sitive association between VAT and bone structural parameters at the distal tibia and radius using high-resolution peripheral quantitative computed tomography (HR-pQCT)2. Saarelai nen et al. evaluated the participation of fatty tissue in BMD, finding a positive association between BMD at the lumbar spine and trunk fat mass in postmenopausal women6. However, despite this supposed beneficial effect, Hind et al. reported that VAT increased the odds of any grade VF in women (VAT: OR = 2.50, p = 0.002)7. These findings highlight the inconsistency in the link between bone tissue and adipose tis sue.
Different authors tried to identify the role of adipose tissue in the physiopathogenesis of os teoporosis. Among the beneficial effects, there is a greater production of 17β-estradiol levels and higher mechanical loads, which may have a posi tive effect on bones8. In addition, adiponectin and leptin, secreted by adipose tissue, would show a beneficial effect on bone mineral due to their abi lity to stimulate osteoblasts9.
On the other hand, it is known that obese people have lower levels of vitamin D and that, depen ding on the obesity phenotype; they induce the release of cytokines that can affect bone health10. Although our study has limitations, among them we can mention that we did not obtain bioche mical and therapeutic data and we do not know the level of physical activity, to the best of our knowledge, there is no local information on the relationship between adipose tissue and its distri bution with bone mass. Therefore, it is important for us to be able to disseminate these results and encourage future research in this field.
